An Improved Analytical Tuning Rule of a Robust PID Controller for Integrating Systems with Time Delay Based on the Multiple Dominant Pole-Placement Method

An improved analytical tuning rule of a Proportional-Integral-Derivative (PID) controller for integrating systems with time delay is proposed using the direct synthesis method and multiple dominant pole-placement approach. Different from the traditional multiple dominant pole-placement method, the desired characteristic equation is obtained by placing the third-order dominant poles at −1/λ and placing the second-order non-dominant poles at −5/λ (λ is the tuning parameter). According to root locus theory, the third-order dominant poles and the second-order non-dominant poles are nearly symmetrically located at the two sides of the fifth-order dominant poles. This makes the third-order dominant poles closer to the imaginary axis than the fifth-order dominant poles, which means that, possibly, better performances can be achieved. Analytical formulas of a PID controller with a lead-lag filter are derived. Simple tuning rules are also given to achieve the desired robustness, which is measured by the maximum sensitivity (Ms) value. The proposed method can achieve better performances and maintain better performances when there exist parameters’ perturbation compared with other methods. Simulations for various integrating processes as well as the nonlinear continuous stirred tank reactor (CSTR) model illustrate the applicability and effectiveness of the proposed method

Tracking Formation and Decomposition of Abacus-Ball-Shaped Lithium Peroxides in Li–O₂ Cells

Study of formation and decomposition of Li₂O₂ during operations of Li–O₂ cells is essential for understanding the reaction mechanism and finding solutions to improve the cell performance. Using vertically aligned carbon nanotubes (VACNTs) directly grown on stainless steel meshes as the cathodes in the Li–O₂ cells with dimethoxyethane (DME) electrolytes, nucleation, growth, and decomposition processes of the Li₂O₂ in the first cycle are clearly visualized. Through cycles with the controlled discharge and charge capacities, the abacus-ball-shaped Li₂O₂ and the rust-like carbonates simultaneously formed around the VACNTs are further identified. It is indicated that the increasing coverage of carbonates on the cathode surface suppresses the formation of Li₂O₂, which maintains the shape of abacus ball. When the VACNT surfaces are predominantly covered by the carbonates, the cells tend to terminate

Fabrication and characterization of a piezoelectric energy harvester with clamped-clamped beams

This work presents a piezoelectric energy harvester with clamped-clamped beams, and it is fabricated with MEMS process. When excited by sinusoidal vibration, the energy harvester has a sharp jumping down phenomenon and the measured frequency responses of the clamped-clamped beams structure show a larger bandwidth which is about 56Hz, more efficient than that with cantilever beams. When the exciting acceleration ac is 12m/s2, the energy harvester achieves to a maximum open-circuit voltage of 94mV on one beam. The load voltage is proportional to the load resistance, and it increased with the increase of load resistance. Connected four beams in series, the output power reaches the maximum value of 730 nW and the optimal load is 15KΩ to one beam

Dynamic evolution of volatile organic compounds in infant formula during storage: Insights from gas chromatography-ion mobility spectrometry

The flavor profile of infant formula (IF) determines its overall acceptability and palatability, significantly impacting its desirability for infants, while the presence of off-flavors challenges the feeding experience and IF quality, even may lead to the rejection by infants. In this study, the dynamic changes in volatile organic compounds (VOCs) during 12 weeks of IF storage at 4 °C–60 °C were monitored by Gas chromatography-ion mobility spectrometry (GC-IMS) for capturing the fingerprints of VOCs. The GC-IMS revealed that a total of 44 VOCs, including acids, alcohols, aldehydes, esters, ketones, and furans. The alternative principal component analysis (PCA) and Sankey diagram in this study offered a comprehensive tracing of the dynamic changes in VOCs, providing valuable implications for the optimization of IF quality control, assessment for validity period and origin tracking in the food industrial

Sustainable Interfaces between Si Anodes and Garnet Electrolytes for Room-Temperature Solid-State Batteries

Solid-state batteries (SSBs) have seen a resurgence of research interests in recent years for their potential to offer high energy density and excellent safety far beyond current commercialized lithium-ion batteries. The compatibility of Si anodes and Ta-doped Li₇La₃Zr₂O₁₂ (Li_6.4La₃Zr_1.4Ta_0.6O₁₂, LLZTO) solid electrolytes and the stability of the Si anode have been investigated. It is found that Si layer anodes thinner than 180 nm can maintain good contact with the LLZTO plate electrolytes, leading the Li/LLZTO/Si cells to exhibit excellent cycling performance with a capacity retention over 85% after 100 cycles. As the Si layer thickness is increased to larger than 300 nm, the capacity retention of Li/LLZTO/Si cells becomes 77% after 100 cycles. When the thickness is close to 900 nm, the cells can cycle only for a limited number of times because of the destructive volume change at the interfaces. Because of the sustainable Si/LLZTO interfaces with the Si layer anodes with a thickness of 180 nm, full cells with the LiFePO₄ cathodes show discharge capacities of 120 mA h g^–1 for LiFePO₄ and 2200 mA h g^–1 for the Si anodes at room temperature. They cycle 100 times with a capacity retention of 72%. These results indicate that the combination between the Si anodes and the garnet electrolytes is a promising strategy for constructing high-performance SSBs

Formation of Nanosized Defective Lithium Peroxides through Si-Coated Carbon Nanotube Cathodes for High Energy Efficiency Li–O₂ Batteries

The formation and decomposition of lithium peroxides (Li₂O₂) during cycling is the key process for the reversible operation of lithium–oxygen batteries. The manipulation of such products from the large toroidal particles about hundreds of nanometers to the ones in the scale of tens of nanometers can improve the energy efficiency and the cycle life of the batteries. In this work, we carry out an in situ morphology tuning of Li₂O₂ by virtue of the surface properties of the n-type Si-modified aligned carbon nanotube (CNT) cathodes. With the introduction of an n-type Si coating layer on the CNT surface, the morphology of Li₂O₂ formed by discharge changes from large toroidal particles (∼300 nm) deposited on the pristine CNT cathodes to nanoparticles (10–20 nm) with poor crystallinity and plenty of lithium vacancies. Beneficial from such changes, the charge overpotential dramatically decreases to 0.55 V, with the charge plateau lying at 3.5 V even in the case of a high discharge capacity (3450 mA h g^–1) being delivered, resulting in the high electrical energy efficiency approaching 80%. Such an improvement is attributed to the fact that the introduction of the n-type Si coating layer changes the surface properties of CNTs and guides the formation of nanosized amorphous-like lithium peroxides with plenty of defects. These results demonstrate that the cathode surface properties play an important role in the formation of products formed during the cycle, providing inspiration to design superior cathodes for the Li–O₂ cells

Monodispersed Carbon-Coated Cubic NiP₂ Nanoparticles Anchored on Carbon Nanotubes as Ultra-Long-Life Anodes for Reversible Lithium Storage

In search of new electrode materials for lithium-ion batteries, metal phosphides that exhibit desirable properties such as high theoretical capacity, moderate discharge plateau, and relatively low polarization recently have attracted a great deal of attention as anode materials. However, the large volume changes and thus resulting collapse of electrode structure during long-term cycling are still challenges for metal-phosphide-based anodes. Here we report an electrode design strategy to solve these problems. The key to this strategy is to confine the electroactive nanoparticles into flexible conductive hosts (like carbon materials) and meanwhile maintain a monodispersed nature of the electroactive particles within the hosts. Monodispersed carbon-coated cubic NiP₂ nanoparticles anchored on carbon nanotubes (NiP₂@C-CNTs) as a proof-of-concept were designed and synthesized. Excellent cyclability (more than 1000 cycles) and capacity retention (high capacities of 816 mAh g^–1 after 1200 cycles at 1300 mA g^–1 and 654.5 mAh g^–1 after 1500 cycles at 5000 mA g^–1) are characterized, which is among the best performance of the NiP₂ anodes and even most of the phosphide-based anodes reported so far. The impressive performance is attributed to the superior structure stability and the enhanced reaction kinetics incurred by our design. Furthermore, a full cell consisting of a NiP₂@C-CNTs anode and a LiFePO₄ cathode is investigated. It delivers an average discharge capacity of 827 mAh g^–1 based on the mass of the NiP₂ anode and exhibits a capacity retention of 80.7% over 200 cycles, with an average output of ∼2.32 V. As a proof-of-concept, these results demonstrate the effectiveness of our strategy on improving the electrode performance. We believe that this strategy for construction of high-performance anodes can be extended to other phase-transformation-type materials, which suffer a large volume change upon lithium insertion/extraction